The invention relates to an apparatus for displaying information comprising at least one display element which includes:                a fluid, the surface energy thereof may be varied by means of an electric field;        a first and a second volume for receiving said fluid, wherein only the first volume is visible and the volumes are separated by a non-transparent intermediate layer; and        a fluidic transition between said first and said second volume,wherein said first volume is arranged between an optically transparent cover layer and said non-transparent intermediate layer and said second volume is arranged between said intermediate layer and a final layer and all layers are parallel across their entire area. Such systems feature by their bistability with respect of both intended locations of the fluid, either in the one or in the other volume. Consequently, no further energy input is necessary when the fluid has reached the desired volume to maintain it stably therein.        
Such fluidic displays are well known from the prior art. Principally all of them always use a plurality of display elements or image dots, also referred to as pixels, mostly arranged in rows and columns and individually controllable, to display a complex image. It is characterizing for fluidic displays that one or more moveable fluids serve to make each single image dot visible. Due to the fact that for making the image dot visible transport of the respective fluid from one reservoir into a visible region of the display and back therefrom is necessary, the known systems often include pumps or realize the fluid transport with the aid of the effect of electro wetting (“electro wetting”). Since for the last mentioned alternative movement of the fluid is based on the possibility to influence the surface energy of a fluid by means of an electric field, such apparatus are in particular characterized in that use of moveable parts is not required.
As already mentioned, it is always mandatorily required for display apparatus which are based on making an image dot visible with the aid of a moveable fluid that the fluid in case that it must not be visible can be stored in a capacity volume or reservoir which is not visible for the viewer. For known systems it is a consequence that the display apparatus in a dimension perpendicular to the viewing plane comprises a non negligible thickness or, if the reservoirs or non visible fluid capacity volumes are arranged in the viewing plane, the display element comprises a decreased use of area and therefore pixel density and consequently lower resolution.
Display elements known from the prior art often show saturation levels varying across the display area which are induced by the fact that fluid layers of varying thickness are present in the visible part of the display element. Thicker layers do not only appear more intensely coloured than thinner ones, but moreover also darker.
A further disadvantage of the known systems is related to the problem that the fluids used in the display do not only move when actually desired, but for example also when in non predictable manner occurring mechanical forces act on the display element during operation. In the most simple case this may already occur by tilting the display element, so that the influence of gravity to the fluids contained therein will change.
WO 2009/036272 A1 discloses an apparatus of the aforementioned type, comprising a visible area, a reservoir as well as a polar and a non polar fluid, wherein respectively one of the fluids dependent on a charged electric field is present either in the visible region or in the reservoir. Due to the comparably low degree of symmetry of the disclosed display elements these are not suitable to be combined as space saving as possible to form a display apparatus.
It is therefore the object of the invention to propose a display element which comprises an optimized utilization of space, possesses a uniform colour saturation across the entire area and is not sensitive to mechanical interference.